1. A Field of the Invention
The present invention is directed to a process of efficiently fabricating a three-dimensional object from a light curable liquid resin.
2. Description of the Prior Art
A small quantity of product models or prototypes can be fabricated without using molds or machining tools in accordance with a process of fabricating a three-dimensional object by the use of a light curable liquid resin. For example, there is a process disclosed in Japanese Patent Early Publication KOKAI! No. 63-141724. This process utilizes a vessel containing a volume of a light curable liquid resin and a movable platform. After the platform is lowered sufficiently below a liquid level of the liquid resin in the vessel, it is lifted to position an upper surface of the platform or previously cured layer just below the liquid level, so that a liquid resin coat having a desired thickness is formed on the upper surface. Subsequently, a laser beam is radiated to the liquid resin coat along a predetermined pattern to obtain a cured resin layer on the upper surface of the platform or the previously cured layer. By repeating the above explained steps, a plurality of cured resin layers are superimposed on the platform to obtain a three-dimensional object of an intended configuration.
However, there is a problem that it is difficult to precisely control the thickness of the liquid resin coat. That is, as the platform is lifted to position the upper surface of the platform or the previously cured layer just below the liquid level of the liquid resin, an excess amount of the liquid resin on the upper surface flows into the circumference of the platform to form the resin coat thereon. However, since the liquid resin is a high viscosity, it takes an extended time to transfer the excess amount of the liquid resin to the circumference of the platform. In other words, it takes the extended time to obtain the resin coat having a uniform thickness. Since the three-dimensional object is fabricated by repeating the steps of forming the resin coat and radiating the laser beam to the resin coat, such a loss of time in this process would cause a low production rate of the three-dimensional object. In particular, as the resin coat having a thinner thickness is desired, a larger amount of the liquid resin has to be removed from the platform. In addition, as a difference of height between a top surface of the resin coat and the surrounding liquid level of the liquid resin in the vessel, that is, a difference of potential energy therebetween, is smaller, it would take more extended time to obtain the resin coat having the thin thickness on the upper surface of the platform or the previously cured layer.
A process for improving the above problem is proposed in U.S. Pat. No. 5,238,614. The process utilizes a vessel 60D containing a volume of a light curable liquid resin 10D and a vertically movable platform 30D for mounting a three-dimensional object to be fabricated, as shown in FIG. 14A. After the platform 30D is lowered sufficiently below a liquid level of the liquid resin bed in the vessel 60D, as shown in FIG. 14B, it is lifted above the liquid level, as shown in FIG. 14C, such that most of the liquid resin 10D on the platform 30D rapidly drops into the vessel 60D through the circumference of the platform 30D to leave a liquid resin coat 11D on the platform 30D. A thickness of the resin coat 11D is greater than a desired thickness thereof. An excess amount of the liquid resin 10D of the resin coat 11D is removed to obtain the desired thickness thereof by sweeping a doctor blade 80D horizontally across the resin coat 10D, as shown in FIG. 14D. Subsequently, the platform 30D is immersed again into the liquid resin 10D in the vessel 60D so as to place a top surface of the resin coat 11D at the approximately same level as the surrounding liquid level of the liquid resin 10D in the vessel 60D, as shown in FIGS. 14E and 14F. A light beam 90D is radiated to the resin coat 11D along a predetermined pattern to obtain a cured resin layer 40D on the upper surface of the platform 30D or previously cured layer 40D, as shown in FIG. 14G. The above explained steps are repeated to fabricate the three-dimensional object on the platform 30D.
However, there are another problems with respect to the production rate and the accuracy of the three-dimensional object. That is, after the platform 30D is lifted above the liquid level so as to separate the liquid resin 10D on the platform 30D from the liquid resin 10D in the vessel 60D, the excess amount of the liquid resin on the platform 30D is removed by the doctor knife 80D to obtain the liquid resin coat 11D having the desired thickness. In this time, the periphery of the resin coat 11D is provided with a round edge 12D, as shown in FIG. 14D, which is caused by the effect of a surface tension of the liquid resin 10D. Immediately after the platform 30D is immersed into the liquid resin 10D in the vessel 60D so as to place the top surface of the resin coat 11D at the approximately same level as the liquid level in the vessel 60D, a gap X is generated between the round edge 12D of the resin coat 11D and the surrounding liquid resin 10D in the vessel 60D, as shown in FIGS. 14E and 16A. Though the gap X disappears within a relatively short time because only a minimum flow amount of the liquid resin 10D is necessary to fill the gap X, as shown in FIGS, 16B to 16D, it is desired to save the time required for eliminating the gap X from the viewpoint of enhancing the production rate of the three-dimensional object. If the light beam is radiated to the liquid resin coat 11D before completely eliminating the gap X, the residual round edge of the resin coat 11D would be the cause of a low accuracy or a considerable deformation of the three-dimensional object.
In addition, when the platform 30D is lifted above the liquid level, it is thought that the excess amount of the liquid resin 10D on the platform 30D rapidly drops into the vessel 60D through the circumference of the platform 30D. As a result, a surface of the liquid resin 10D in the vessel 60D would be fretted by the dropped liquid resin from the platform 30D, as shown in FIG. 15. When the resin coat 11D on the platform 30D is immersed into the liquid resin 10D in the vessel 60D, thus fretted surface of the liquid resin 10D would prevent to form a flat surface of the resin coat 11D which is placed at the approximately same level as the liquid level 10D of the liquid resin 10D in the vessel 60D. Consequently, it would require more extended time for smoothing the fretted surface of the liquid resin 10D. If the light beam 90D is radiated to the resin coat 11D without sufficiently smoothing the fretted surface of the liquid resin 10D, the cured resin layer 40D having a uniform thickness could not be obtained on the platform 30D or the previously cured resin layer 40D.